136 Muller's specimens had the point of the postero-iateral arms red coloured (and, judging from his figure, quite conspicuously so), and the young star also had a big red patch in the middle of the dorsal side ; the specimens observed by me had only a faint yel- lowish tint in the end of the arms and in the middle of the dorsal side of the young star, the larva being otherwise niilky white and opaque, so that the skeleton could not be seen distinctly without applying some clearing fluid. This diversity in colour being the only notable difference between the two larvæ it seems justifiable to regard them as identical or, at least, as belonging to two very closely related species. The faet that there were no dis- tinet ciliated bands along the postero-iateral arms, together with the peculiar opaqueness of the larva, would seem to indicate that this larva does not have the full pluteus shape, but belongs to the rudimentary larva! forms. This cannot, however, be decided, before larvæ have been observed in which the metamorphosis is less advanced than in those observed till now. The occurrence of this larval form both in the Adriatic and at the coast of Bohusian allows a suggestion about the Ophiuroid to which it must belong. The following Ophiuroids are common to the Scan- dinavian seas and the Adriatic: Ophiiira teæturaia, O. albida, O. (iffinis, Amphiura filiformis, A. Chiajei, Aniphipholis squamata, Ophiothrix fragilis and probably also Ophiocoma nigra. Of these species one, Amph. squamata, is viviparous and thus cannot come into consideration. The larvæ of Ophiiira teæturata, O. albida, Am- phiura filiformis (see below) and Ophiothrix fragilis are known, these species being thus also eliminated ; likewise Ophiocoma ni- gra, evidently, is out of question.') Amphiura Chiajei and Ophiura affmis thus alone can come into consideration as species to which this larva could belong. Joh. Muller, in faet, suggested that the larva might possibly belong to Amphiura Chiajei (he names it incorrectly Ophiolepis SiindeDalli; as it is especially noticed that the species has two tentacle scales, it is beyond doubt that the species meant is Amph. Chiajei), his reason for this suggestion being that the dorsal side of the disk in this species is red as in ') Th. M orte n se n. On the development of some British Echinoderms. Journ. Mar. Biol. Assoc. N. Ser. X. 1913. p. 12.
137 the developing star of the larva. This reason, evidently, is of very small weight only, and there is, at least, one faet which appears to show that the larva cannot belong to this Ophiuroid. Amphiiira Chiajei was found at Kristineberg to have its breeding season only from the middle of September, no specimens with ripe genital pro- ducts having been observed before that time. But, as stated above, the larvæ were found in the beginning of August, and not later. Everything thus points towards Ophiura affmis as the species to which this larva belongs. It is true, the species is not recorded as occurring at Bohusian ^), but I found it there in a dredging off „Smedjan" on the 19th August 1918 (together with Ophiura ro- busta Ayres, which was likewise unknown from the coast of Bo- husian). The specimens were noted to contain no ripe sexual pro- ducts. This faet is also in accordance with the observations on the larvæ, which were all in the metamorphosis stage, so that the breeding season of the species should be about the middle of July. Provided the reference of this larva to Ophiura affinis be cor- rect, this will add considerably to the remarkable diversity among the larvæ of apparently so closely related species as Ophiura texturata and albida, the difference of these larvæ being so con- spicuous that it is hard to understand, how they can belong to the same genus. In case that — as I think there is some reason to suppose — Ophiophiieus compressus should prove to belong 10 Ophiura Sarsi, this diversity will be still more remarkable. The conspicuous difference in regard to colour between the Adriatic specimens of this larva and those from Bohuslån might indicate that the Adriatic form of Ophiura affinis differs to some extent from the Scandinavian form. I was therefore very much interested in learning from my friend, Professor Koehler in Lyon, that he was inclined to regard the Adriatic form of Ophiura af- finis (the Ophiura Gruhei Heller) as at least a distinct variety; a careful comparison of the single specimen from the Adriatic at my disposal with specimens from the Scandinavian seas convinced me of the correctness of Koehler's view. Indeed, I should be much Hj. Théel. Om utvecklingen af Sveriges Zoologiska Hafstation Kri- stineberg och om Djurlifvet i angransande Haf og Fjordar. Arch for Zoologi. Bd. IV. 1907.